48 PATHOGENIC BACTERIA. Rarely, the presence of one species of microorganism entirely eradicates another species. Hankin found that the Micrococcus Ghadialli destroyed the typhoid and colon bacilli, and suggested the use of this coccus to purify waters polluted with typhoid.1 (z) Temperattire.—The question of temperature is of importance from its bearing upon sterilization. Accord- ing to Frankel, bacteria will scarcely grow at all below 16° and above 40° C. • The researches of Fliigge show that the Bacillus sub- tilis will grow very slowly at 6° C., and as the tempera- ture is elevated it is said that until 12.5° C. is reached fission does not occur oftener than every four or five hours. When 25° C. is reached the fission occurs every three-quarters of an hour, and at 30° C. about every half hour. Most bacteria die at a higher temperature than 60- 75° C. The spores can resist boiling water, but are killed by dry heat if exposed to 150° C. for an hour or to 175° C. for five to ten minutes. Freezing kills many, but not all bacteria, but does not affect the spores at all. Most bacteria grow best at the ordinary temperature of a comfortably heated room, and are not affected by its occasional slight changes. Some, chiefly the pathogenic forms, are not cultivable except at the temperature of the animal body (37° C.); others, like the tubercle bacil- lus, grow best at a temperature a little above that of the body—40° C. Variations in the amount of oxygen, temperature, moist- ure, etc., beyond what have been described, are prej- udicial to the growth and development of bacteria, first inhibiting their growth, thus tending toward their de- struction. In the practical application of our knowledge of the biology of the bacteria we constantly make use of such precautions as removing from surgical dressings, sponges, etc., every substance that can possibly afford nutriment to bacteria, and heating such materials, as well 1 Brit. Med. Jour., Aug. 14, 1897, p. 418.